If you want to contribute to the Radare2 book, you can do it at the Github repository. Suggested contributions include:
- Crackme writeups
- CTF writeups
- Documentation on how to use Radare2
- Documentation on developing for Radare2
- Conference presentations/workshops using Radare2
- Missing content from the Radare1 book updated to Radare2
Please get permission to port any content you do not own/did not create before you put it in the Radare2 book.